The present invention relates to a system for controlling the position of a marine drive unit and, more particularly, to a system for automatically positioning a drive unit to optimize speed at a given throttle setting.
The drive units for marine propulsion devices, including outboard motors and stern drives, are supported from the boat transom by a drive mounting assembly. Various types of drive mounting assemblies are known, as for example a transom bracket for mounting an outboard motor directly on a boat transom or a gimbal ring assembly for similarly mounting a stern drive unit directly to the transom. Typically, a drive unit mounted directly on the boat transom may be trimmed by pivoting it about a generally horizontal axis in order to position the propeller and optimize thrust with respect to the plane of the boat. However, the vertical position of the drive unit usually cannot be changed beyond the somewhat limited amount which inherently results from the trimming operation. Therefore, the drive unit must typically be mounted in a compromise position at a fixed height with respect to the transom which will provide the best performance. Another type of drive mounting assembly is one which is capable of selectively supporting an outboard motor in either a raised or a lowered position aft of the boat transom. Many of these transom extension types of mounting assemblies are of the general type which include a pivotally connected quadrilateral linkage, generally in the form of a parallelogram.
Transom extension mounting assemblies have become increasingly popular on high performance boats powered by outboard motors, such as bass boats, where a lower position of the motor improves initial boat acceleration and a higher position enhances top speed by reducing gear case drag. Additionally, a higher motor position reduces draft, thereby enhancing shallow water operation. It is further known that relocating the motor aft of the transom improves the handling characteristics of most boats at high speeds. These devices also allow the boat to be built with a higher transom for improved safety in following wave conditions, thereby allowing boat builders to manufacture a common hull and transom design for both outboard and stern drive applications.
Examples of transom extension mounting assemblies for outboard motors, which support the motor spaced from the boat transom, are disclosed in the following U.S. Pat. Nos.: 2,782,744; 3,990,660; 4,013,249; 4,168,818; 4,673,358; and 4,682,961. The first four of the foregoing patents disclose apparatus which is utilized to raise the motor vertically and the latter two patents describe apparatus which is utilized to trim the propeller and tilt the motor up and out of the water about a generally horizontal axis. In addition, U.S. patent applications Ser. No. 092,168, filed Sept. 2, 1987; Ser. No. 100,216, filed Sept. 23, 1987; Ser. No. 103,508, filed Oct. 1, 1987; Ser. No. 172,399, filed Mar. 24, 1988; and an application entitled "Combined Trim,. Tilt and Lift Apparatus for a Marine Propulsion Device" filed Apr. 14, 1988, all of which are assigned to the assignee of this application, disclose outboard motor transom extension mounting assemblies which utilize a quadrilateral linkage arrangement to raise and lower the motor with respect to the transom. The quadrilateral linkage comprises four pivotally connected links forming a collapsible linkage the movement of which effects vertical movement of the motor. Various of the foregoing co-pending applications disclose means for controlling the movement and positioning of transom extension mounting assemblies to avoid hazardous or undesirable operating conditions. The disclosed control systems operate automatically to lift or lower the motor with respect to the transom until the hazardous or undesirable operating condition is eliminated.
U.S. Pat. No. 4,318,699 discloses a system for automatically trimming a marine drive unit in response to a sensed operating condition, such as engine speed. A trimming operation involves tilting the drive unit about a horizontal axis to position the drive unit for on-plane and off-plane operation of the boat. The drive is typically trimmed out at high speeds and trimmed in at lower speeds. The system of the foregoing patent is automatically responsive to move the drive unit to preselected trim positions characteristic of the boat on which it is used.
U.S. Pat. No. 4,718,872 describes a system for automatically adjusting the trim of a marine drive unit by sensing an increase in boat speed and adjusting the trim until the boat speed ceases to increase. The automatic control system is operative to incrementally move the drive unit in one direction as long as the movement results in an increase in speed and then to move the drive unit in the opposite direction as long as the adjustment results in an increase in speed. The control system thus hunts for optimal adjustment by trimming the drive unit back and forth in both directions until maximum boat speed at a particular throttle setting is achieved. However, basing an automatic trim adjustment on the occurrence of any increase in speed (or the absence thereof) may result in excessive hunting by the system and trim changes based on small changes in speed which are too insignificant to make any practical difference. In addition, although proper trim control has a significant impact on speed optimization, vertical lifting and/or lowering of the drive unit can also significantly affect speed optimization. Furthermore, trim and lift drive systems in a boat are generally independent and manual adjustment of each of them by an operator to attain optimum speed is somewhat difficult and requires substantial skill.
It would be desirable, therefore, to have a system for automatically adjusting both trim and lift of a drive unit to attain optimum speed at a particular throttle setting. In addition, it would be desirable to have a system which is relatively immune from excessive hunting and position changes which do not have a practical effect on boat speed.